U.S. Rep. John Garamendi tells The Associated Press that the lockdown went into effect at Travis Air Force Base on Wednesday after someone reported a possible gunshot.

Garamendi, who was briefed on the situation, says there was a training exercise underway at the base at the time and "someone took that to be an active shooter."

The Solano County Office of Emergency Services posted on Facebook that there is no active shooter and the response has been canceled.

The base is off Interstate 80, approximately 45 miles northeast of San Francisco.

On their Facebook page, the U.S. military base located in Fairfield in Solano County, had characterized the situation as "real world security incident".

The base issued a security alert shortly after 3:30 p.m. Wednesday asking people to shelter in place and to lock doors and windows.

Marie Lowe, a civilian who answered the phone at the base's public affairs office, said details were sketchy as the situation was investigated.

The lockdown comes on the same day that the base had been conducting security lockdown exercises, but officials say the incident is real and not part of the drill.

The main gate at the base was closed for some time, according to Fairfield police said.

The simulated real word security drill was scheduled to take place today and Thursday.

Civilian Bobbi Textor said she is one of at least a half-dozen people who are answering the flood of phone calls to the base about the ironic turn of events.

A source at the base, who wanted to remain anonymous, texted KTVU and said an announcement over the loudspeaker said, "base lockdown, lock all doors and windows. Turn off all lights" due to a real world live shooter situation".